JPH0747119B2 - Device for injecting low vapor pressure substances into low pressure or vacuum systems - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a device for accurately injecting low vapor pressure substances into a low pressure or vacuum system.

[Conventional technology]

In vapor phase epitaxy and molecular beam epitaxy growth using a gas source, the semiconductor compound is in a gaseous state of aggregation in a low pressure or vacuum system to grow a thin film on the surface of the cryogen heated there. Is injected into. For this purpose, there is a need for a device for obtaining a particle flow that can be accurately distributed in sufficient quantity at the outlet opening to the vacuum chamber. The outflow rate must be very precisely adjustable, especially when using several gas supply pipes to bring various semiconductor compounds, in particular metal-organic compounds, into the injection chamber in a predetermined stoichiometric ratio.

Conventionally, in such devices, pure vapor of the substance to be injected has been injected directly into the vacuum system under pressure control. However, this is due to the unavoidable conduction resistance, and substances with a saturated acid-saturated vapor pressure (for example, triethylindium at about 20 ° C and about 0.25 mbar).
If only) then only a very small mass flow is obtained. Conventionally, in order to obtain a large substance flow, a carrier gas, for example, hydrogen is introduced into a container containing a substance to be injected (so-called bubbling), and this carrier gas is collected in a gaseous state in the upper part of the container. It had to be mixed with the substances, and this mixture had to be introduced under some pressure into a vacuum chamber maintained at a low pressure or vacuum by a pump system.

Therefore, in the case of such a device, it is necessary to adjust the flow-through gas amount. This is typically done by a mass flow controller that measures the flow-through carrier gas in front of the container containing the semiconductor compound. This method has the drawback that the measurement accuracy of the mass flow controller is too low for small flow rates (1 cm ³ / min or less). On the other hand, the pressure in the pipe can be measured extremely accurately.

[Problems to be Solved by the Invention]

An object of the present invention is to provide a device capable of accurately distributing and injecting a substance having a low vapor pressure into a low pressure or vacuum system at a sufficient substance flow rate.

[Means for Solving the Problems]

According to the invention, this object comprises at least one low-pressure / vacuum quality and at least one container for containing the substance to be injected, in liquid or solid form, into this container reaching close to its bottom. A carrier gas supply line and an outlet line above the container for the mixture of the carrier gas and the substance to be injected which is in the gas phase and exiting from the underside of the lid, low pressure Alternatively, in a gas system for accurately injecting a substance having a low vapor pressure into a vacuum system, a first control valve is provided in a supply pipe and a second control valve is provided at an end of an outlet pipe, and a second control valve is provided. Is provided with an injection pipe for guiding the gas flow to the low pressure / vacuum quality, the outlet pipe is provided with a first pressure measurement point, the injection pipe is provided with a second pressure measurement point, and the first pressure measurement point is provided. The first pressure measuring device A second pressure measuring device is connected to the portion, a first signal line from the first pressure measuring device to the first control valve, and a second signal line from the second pressure measuring device to the second control valve. Can be achieved by adjusting the pressure at the measuring point via the control valve, which control valve is controlled via a signal line by the pressure measuring device.

That is, the device according to the present invention is configured as follows.
A container sized therefor is used to contain the substance to be injected, for example a semi-metallic organic compound in the liquid state of aggregation. A supply pipe and an outlet pipe through which the carrier gas flows are provided to the container. A control valve is incorporated in each of the supply pipe and the pipe between the container and the vacuum chamber. The control valve in the carrier gas supply line is controlled via the electronic control unit. This control device mainly consists of a pressure measuring device which measures the pressure in the pipe coming out of the container and compares it with a predetermined set value. Behind this control valve between the container and the vacuum chamber, a corresponding adjusting device is provided. In this case, the pressure measuring point is set just behind the control valve.

[Action effect]

It should be noted in explaining the operation of the device according to the present invention that the total pressure in the outlet pipe coming out of the container depends on the partial pressure of the carrier gas and that of the substance to be injected in the gaseous state of aggregation. It consists of pressure. However, it is the particle flow, not the pressure, that is important to the operation of this device. The flow rate is a function of pressure. Depending on the gas density and the geometry of the pipe, viscous or molecular flows or their intermediate flows occur. Viscous flow is represented by the ratio of flow rate to the square of pressure, and molecular flow or Knudsen flow is represented by the ratio of flow rate and pressure. For pressures in the range of about 0.1 to 10 mbar, there is generally a ratio between the flow rate and a power that is greater than one. Therefore, the relationship between flow rate and pressure is hyperlinear. As a result, the flow rate increases remarkably in proportion to the increase in pressure in the pipe. For example, squared, in the absence of carrier gas, the flow rate is proportional to the square of the vapor pressure of the substance to be injected. When this gas is mixed with a carrier gas having the same partial pressure, the total pressure is twice as high as in the first case. However, since the flow rate is related to the square of the pressure, the total flow rate becomes four times. The total flow rate consists of equal parts carrier gas flow rate and gaseous injectate flow rate. Thus, the flow rate of the substance can be doubled by adding the carrier gas. If it is less than the square, i.e. in the case of a proportional relationship between the flow rate and the exponential pressure between an index of 1 and 2, the effect produced is correspondingly weakened. In the case of low vapor pressure substances, it is possible in this way to increase the flow rate of the substance to be injected by pumping the carrier gas.

The vapor pressure of the substance to be injected is kept constant by keeping the container with the substance at a constant temperature in a warm bath or the like. The measurement of the total pressure controls a control valve built into the supply line for the carrier gas, and in this way the total pressure is either kept constant or is adjusted to the set value each time. The second control valve individually controls the pressure of the gas mixture and thus of the particle stream entering the vacuum chamber.

〔Example〕

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

The container 1 is used for containing a substance to be injected in a liquid or solid form. A carrier gas supply pipe 2 communicates with the container 1. The supply pipe 2 is open close to the bottom of the container 1. An outlet pipe 3 extends from the container 1, and its opening is located above the container 1 and below the cover or the closing lid. In this way, the carrier gas can be introduced into the substance in the container 1 via the supply pipe 2. In that case, the carrier gas rises in the substance in the form of bubbles, is mixed with the substance in the vapor phase state due to equilibrium of vapor pressure, and is discharged from the container 1 through the opening of the outlet pipe 3.

A first control valve 7 is installed in the supply pipe 2 and a second control valve 11 is installed at the end of the outlet pipe 3. Container 1 and this second
A first pressure measuring point 5 is provided between the control valve 11 and the control valve 11. A first pressure measuring device 4, which is connected to this pressure measuring point 5, measures the pressure at this point, compares this pressure with a target value and, via a first signal line 6, a first control valve 7 is controlled, whereby the gas pressure at the first pressure measurement point 5 is adjusted to a predetermined pressure and kept constant. This is + 0.1% when using an accurate pressure detector
It can be performed with the above accuracy.

The outlet pipe 3 is connected behind a second control valve 11 to an injection pipe 13 for introducing gas into a vacuum chamber 12 forming part of a low pressure or vacuum system. The injection pipe 13 is provided with a second pressure measuring point 9 to which a second pressure measuring device 8 is connected. The second pressure measuring device 8 measures the pressure at the location 9 and controls the second control valve 11 via the second signal line 10. With such a control mechanism, the pressure at the second pressure measuring point 9, and hence the particle flow rate, is accurately adjusted to a predetermined value. In that case, the pressure at the second pressure measuring point 9 does not exceed the pressure at the first pressure measuring point 5.

Further according to the invention, an auxiliary bypass 16 for the container 1 is provided. A shutoff valve 14 is incorporated in the supply pipe 2 between the first control valve 7 and the container 1. One pipe branches from the supply pipe 2 between the first control valve 7 and the shutoff valve 14. This pipe opens to the outlet pipe 3 between the container 1 and the second control valve 11 and forms a bypass passage 16. At least one valve 15 is incorporated in the pipe to shut off the bypass 16. Bypass passages to avoid creating dead spaces that will not be washed out
It is advantageous to provide valves at each of the 16 connection points.

An advantageous mode of operation of this device is that the pressure at the first pressure measuring point 5 is set to the first pressure measuring device 4 and the first control valve 7.
The pressure in the injection pipe 13 is detected at the second measuring point 9, and the second pressure measuring device 8, the second signal line 10 and A second control valve 11 is used to adjust the value to the required material flow in each case.

Another advantageous mode of operation is to keep the pressure at the second pressure measuring point 9 constant via the control mechanism and to control the first control valve 7 in response to fluctuations in the pressure at the first pressure measuring point 5. The mechanism consists in changing the ratio of carrier gas to effective gas, in which case the physical property of non-linearity between particle flow rate and pressure is also used.

[Brief description of drawings]

 The drawing is a schematic illustration of a system according to the invention. DESCRIPTION OF SYMBOLS 1 ... Container 2 ... Supply piping 3 ... Outlet piping 4 ... 1st pressure measuring instrument 5 ... 1st pressure measuring location 6 ... 1st signal wire 7 ... 1st control valve 8 ... 2nd pressure measuring instrument 9 … Second pressure measurement point 10… Second signal line 11… Second control valve 12… Low pressure or vacuum chamber 13… Injection piping 14, 15… Shutdown valve 16… Bypass path

Claims (2)

[Claims] 1. At least one low-pressure / vacuum chamber (12) and at least one container (1) for containing a substance to be injected in liquid or solid form, in which the container (1) A carrier gas supply pipe (2) reaching near the bottom and above the container (1) for the mixture of carrier gas and the substance to be injected in the gas phase, exiting from the underside of the lid. In an apparatus for accurately injecting a substance having a low vapor pressure into a low-pressure or vacuum system, which is provided with an outlet pipe (3) which is provided, a first control valve (7) is provided at an outlet of a supply pipe (2). The second control valve (11) at the end of the pipe (3)
Is provided, an injection pipe (13) for guiding a gas flow to the low pressure / vacuum chamber (12) is provided behind the second control valve (11), and a first pressure measurement point is provided at the outlet pipe (3). (5) is provided with a second pressure measurement point (9) in the injection pipe (13),
At the first pressure measuring point (5), the first pressure measuring device (4)
However, the second pressure measuring device (8) is connected to the second pressure measuring portion (9), and the first signal line (from the first pressure measuring device (4) to the first control valve (7) ( 6) is the second signal line (10) from the second pressure measuring device (8) to the second control valve (11).
And the pressure at the measuring points (5, 9) is regulated via the control valves (7, 11), which control signals (7, 11) are signaled by the pressure measuring device (4, 8). Device for injecting a substance of low vapor pressure into a low pressure or vacuum system, characterized in that it is controlled via lines (6, 10). 2. A bypass passage (16) with a valve (15) is provided between the supply pipe (2) and the outlet pipe (3), and the bypass pipe (16) is provided with a bypass passage (16). A shut-off valve (14) is provided at the rear, characterized in that
The described device.